Fuel delivery systems for internal combustion engines, such as spark ignition engines, require a fuel injector pump and a direct-injecting fuel nozzle for delivering fuel directly into the combustion chamber for each of the working cylinders of the engine. The pump includes a pump plunger that reciprocates in a pump pressure cavity. The plunger is driven mechanically by a crankshaft-driven camshaft so that the pumping stroke frequency is directly proportional to engine speed. Such systems further require a precision fuel control valve for establishing and interrupting fuel delivery from the pump to the nozzle, the valve being controlled by a solenoid actuator that in turn is responsive to controlled current pulses in a driver circuit for an electronic engine control system. As the injector pump creates the necessary pressure pulses, the metering of fuel delivery from the injector pump through the nozzles is under the control of the fuel control valve.
The injector pump is supplied with fuel by a fuel supply pump that communicates with the fuel supply side of the injector pump. It operates with a relatively low inlet fuel supply pressure. Fuel circulates continuously through the solenoid-operated fuel control valve as the fuel supply pump distributes fuel to the injector pump.
In a fuel supply system of this kind, it is possible for liquid fuel cavitation to occur, especially at high engine speeds when the injector pump supplies the nozzle with fuel at a relatively rapid rate. Since delivery of a fuel charge to the nozzle occurs with a pulse frequency that is related to engine speed, the inertia created by the mass of the fuel flow may be sufficient to create cavitation in the fuel delivery passage on the upstream side of the nozzle and on the downstream side of the solenoid-operated fuel control valve. Further, a tendency exists for pressure pulses to be fed back to the injector pump, particularly at high engine speeds. The solenoid-operated valve cannot effectively isolate the injector pump from pressure peaks that occur in the fuel delivery passages. If the pressure peaks enter the pump pressure cavity, damage to the pump and premature pump failure may occur because of the pressure forces caused by the pressure peaks.